Agreed hold it on with a rope or bungee.Just make sure it doesn't pop out of the hole (lol).
I run an adapter I made up to the stat housing which will work if your engine has a drive mounted water pump (no impeller on the engine). If you have a Volvo or Bravo with the impeller on the engine, you must connect the water source back at the transom mount, or directly to the impeller itself.